1. Technical Field
The present invention relates generally to imaging apparatus such as printers and copiers that form media into a cylindrical shape for exposure by a rotating light source, and more particularly to a static elimination system for reducing static electrical charges on the surface of media in the imaging apparatus.
2. Background Art
Digital imaging in printers and copiers is accomplished by modulating the intensity of a light beam that forms a writing spot on photosensitive media as the beam moves relative to the photosensitive media. One type of imaging apparatus uses a modulated array of light emitting diodes (LED's) positioned on a write head assembly resident on a rotor which is simultaneously rotated about a fixed axis and linearly translated past stationary photosensitive recording media mounted on the inner surface of a cylindrical "support shoe" to form a plurality of writing spots moving across the photosensitive material in a fast scan direction and in a slow scan direction, such as disclosed in commonly assigned, co-pending U.S. patent application Ser. No. 08/371,241, entitled DIGITAL PRINTER WITH SUPPORT SHOE AND TRANSLATABLE MEDIA GUIDE MEMBER THEREIN filed in the name of M. Bridges on Jan. 11, 1995. The disclosure of the Bridges patent application is hereby specifically incorporated herein by reference.
Static electrical charges are triboelectrically generated on a dielectric material by contact with charged rollers or by frictional contact with stationary guide surfaces necessary to transport the material through a handling apparatus. The build-up of these charges can be a severe problem, particularly in photographic printing, as light produced during static discharge through air will expose the photosensitive surface of the media. Such static electrical charges can cause the material to be attracted to portions of the handling apparatus, thus interfering with proper functioning of the apparatus. Additionally, the static electrical charges may attract dust. Nearby electronics may be susceptible to electrostatic discharge or field induced transients. Finally, there is a need to prevent discharge of static energy from the surface of the media to the LED array, as such discharge may cause improper illumination of the LED's during printing.
Thus, many types of devices have been used to reduce or remove static electricity on a dielectric material. For example, U.S. Pat. No. 4,494,166, which issued to Billings et al. on Jan. 15, 1985, discloses a paper handling apparatus for a printing machine that uses grounded carbon bristle brush static eliminators. Such brushes are well known and widely used. The tips of such brushes need not touch the media. They operate by concentrating field lines so as to locally exceed the breakdown strength of air. The field lines, caused by the charges on the media, will preferably end at the grounded tips of the brush bristles. This is equivalent to a high field strength in the tip region.